Superheterodyne signal receiving system



Jan. 16; 1940.. P, D, LOWELL 2,186,980

SUPERHETERODYNE S IGNAL RECEIVING SYSTEM Filed Sept. 24, 1937 Sheets-Sheet 1 Z I m 28.0Mc. V c

PERCll/AL D. LOWELL.

Jan. 16, 1940. P; D. LOWELL I QSUPERHETERODYNE SIGNAL RECEIVING SYSTEM Filed Sept. 24, 1937 2 Sheets-Sheet 2 Pt'RC/l/AL i0. Lam/ELL,

Patented Jan. 16 1940 UNITED STATES rArsN'r orrlce SUPERHETERODYNE SIGNAL RECEIVING I SYSTEM Percival D. Lwell, Chevy Chase, Md.

Application September 24, 1937, Serial N0.,165,577

7 Claims.

. My invention relates broadly to radio receiving circuits and more particularly to the superhet- :erodyne type of receiver and arrangements for employing a piezo-electric crystal element for v '5 controlling the frequency converting oscillator.

' *as rthefundamenta'l or a harmonicof a piezoelectric crystal controlled oscillator. I

Still anotherobjectof my invention is to provide a superheterodyne circuit arrangement for receiving continuous Wave transmissions, employ- 5 ing converting and beat oscillations derived from a single piezo-electric crystal controlled oscillator.

nstill further :object .of my invention is to provide means for receiving any of a plurality :of signal oscillations of difierent frequencies, em-

.3 p owing as converting oscillations the fundamental and harmonics derived froma single piano-electric crystal controlled oscillator.

Still another object of my invention is to provide arrangements for employing the fundamental and harmonic oscillations derived from a single oscillator to produce desired results of freque'ncy conversion or thelike in a plurality of portions of a radio receiving system without inter- Terence. between the several portions of thesys tom.-

Other and further objects of my invention reside in the circuitarrangements, hereinaftermore .fully described with reference to the accompanying drawings in which: "Figurel is aschematic diagram of one arrangement-for .dual conversion of the signaloscillation, employing a single piezo-electric crystal controlled oscillator; Fig. 2is amodified form of the W circuit of Fig.1; Fig. 3 is :a schematic diagram illustrating a piezo-electric crystal controlled oscillator employed in the reception of continuous wacesignals; and Fig. a is a schematicdiagram showing the furtherarrangement of a piezo-electric crystal .controlledioscillator for the reception of either or both of two signals of-different frequencies. I

The superheterodyne type of radio receiver is highly selective in differentiating radio signals of closely related frequencies, due principally to :5 the intermediate frequency scheme .of amplification, which permits the use of mostv eflicient amplifier designs for the particular intermediate frequency selected. Proper and most effective use of this type of receiver depends, therefore up- 1L0 on the tability of the intermediate frequency wave .which *is produced as the beat of the incoming signal and a local oscillation For frequencies.

of a few megacycles, sufficiently stableconverting oscillators, may be built so that the :frequency .16 I thereof may be varied'over a range equal to the tuning range of the receiver, and intermediate frequency Waves of satisfactory-stabilitybe correspondingly produced.

,y In higher vfrequency ranges however, in order "to maintain high selectivity in the intermediate frequency amplifier, it is "imperative that. the fre- :quency of the conversion oscillator 'be controlled Within extremely narrow limits. Forthis reason,

variable frequency conversion oscillators for ultra-high frequency receiving circuits are .not feasible, and piezo-electric crystal controlled oscillators for the individual signal frequencies received have been'suggested. One .of .the prin-- :cipal difficulties which exist -is the problem of constructing piezo-electric crystal oscillators capable of converting the-ultra-high controlled signal frequencies to the relatively low frequencies 'of intermediate frequency amplifiers. .By the system of my invention this difiiculty isovercome .35

in a practical manner, and numerous variations --.besides those disclosed are contemplated within the scope of my invention. I Referring to the drawings in more detail, Fig. 1 illustrates the antenna at l feeding signali40 energy to thetuned circuit 2 connected with the grid of a first conversion stage 3.

The local heterodyning oscillator comprises the pentode tube shown at 4, having piezo-electric crystal v5 connected with the control grid lo and the screen .45

grid 4b serving as an anode and connected with resonant circuit '6. The output circuit connects with. the anode 4c and includes resonant circuit '1 whichcornprises individual inductances la and lb jointly'tuned by combination with a con-- denser 1c. The inductance la .is included with tuned circuit 2 in the input of the first conversion stage 3, and the output circuit 8 thereof is tuned to'the conversion frequency resulting from beating of oscillations at the signal frequency and I the frequency of the resonant circuit 1. The inductance lb is connected in series with the tuned circuit 8 in the input of a second conversion stage 9, and the output circuit In thereof is tuned to the conversion frequency resulting from beating of the signal having the frequency of tuned circu'lt 8 and an oscillation of the frequency of resonant circuit 1. An intermediate frequency amplifier is coupled to the output circuit ID by suitable means as at I2, and leads to the remainder of a conventional superheterodyne re ceiving system including the second detector and audio frequency amplifying means connected to a reproducer. Suitable operating potentials are supplied to the various electrodes in conventional manner, and it will be understood that the circuits of Fig. l, and all the figures are intended to be schematic and illustrative only of the system arrangements of my invention.

Fig. 1 shows a double frequency conversion superheterodyne receiver where the incoming signal is first converted to a lower frequency by heating with one harmonic of the oscillator and then converted to a still lower frequency, the intermediate frequency by beating again with the same harmonic. In the case of Fig. 1, as an example, take the received signal to be at megacycles. In this ultra-high frequency region it is practically impossible to grind a crystal for a frequency which would beat directly with 60 megacycles to produce an intermediate frequency of 4.0 megacycles, approximately the frequency commonly used under these conditions. In Fig. 1, I have indicated a crystal for operation at 9.3333 megacycles, connected in the control grid circuit of the oscillator tube 4, the screen id therein being tuned to the crystal frequency at resonant circuit 6, thus forming a normal triode crystal oscillator circuit. In the plate output circuit, the resonant circuit 1 constitutes a split harmonic trap circuit tuned to the third harmonic of the crystal or 28.0 megacycles. Section Ta of this trap circuit couples into the grid return of the first conversion stage 3 and the 28.0 megacycle harmonic beats with the incoming signal at 60 megacycles and produces a resultant frequency of 32.0 megacycles which appears in the tuned circuit 8. This tuned circuit is connected also with the grid of the second converand the 28.0 megacycle harmonic beat to produce the intermediate frequency wave of 4.0 megacycles to which the second output'plate circuit I 0 is tuned. From this point on, the circuits are the same as used in common practice.

The circuits of Fig. 2 likewise include the anj tenna I, tuned circuit 2 and first conversion stage 3 having output circuit 8 connected also in the input of a second conversion stage 9. Fig.

2 further shows a third conversion stage I4,

J coupl d with the preceding stage 9 by means of 1 in series with circuits 3 tuned circuit H5. The final tuned output circuit in is connected with the conversion stage M. Fig. 2 differs from Fig. 1 principally in the conversion oscillator, shown in Fig. 2 as a triode I6, having a piezo-electric crystal I! in the grid circuit, and a series of independently tuned circuits in the anode circuit thereof. Tuned circuit I8 is connected in series with circuit 2 in the input of the first conversion stage 3; and tuned circuits l9 and 20 likewise respectively connected and I 5 in the inputs of the second and third conversion stages 9 and I4.

In considering Fig, 2, take for example, the signal frequency to be 60 megacycles and the intermediate frequency to be 4.0 megacycles, as in Fig. l. The 60 megacycle signal is first beat with a 28.0 inegacycle wave which is the third harmonic of a crystal frequency of 9.3333 megacycles, this harmonic being selected by properly tuning the circuit [8 which is part of the grid return of the first conversion stage 3. The plate circuit 8 of the first conversion stage is tuned to 32.0 megacycles, which is the resultant frequency. This resultant frequency is then beat with an 18.6666 megacycle wave, the second harmonic of the crystal frequency, selected in tuned circuit 19, to produce a resultant of 13.3333 megacycles in the tuned output circuit l5 of the second conversion stage. Similarly, this last frequency is beat in the third conversion stage [4 with the fundamental crystal frequency selected in the third tuned circuit 20, and the final resultant or intermediate freqency of 4.0 megacycles appears in the tuned output circuit I 0. From there on the circuit is conventional, as in Fig. 1.

Fig. 3 shows a modified arrangement of the system of my invention employed when a superheterodyne receiver is desired for receiving continuous wave signals with crystal control on both the frequency converting oscillator and the beat frequency oscillator. One crystal is used for both purposes. In this arrangement, an antenna and tuned circuit 2 feed into a radio frequency amplifying stage 2! which is coupled with the conversion stage 23 through means including a resonant circuit 24 which is electromagnetically coupled with the output of the confrequency wave which appears in the output circuit 10'.

Detection of the continuous waves is effected in the detector stage 29, in the grid circuit of which is resonant circuit 30 coupled with the output circuit 10 of the conversion stage 23,

and with tuned circuit 28 of the crystal controlled oscillator which supplies oscillations of proper frequency for beating with the signal waves in the detector 29 to produce an audible signal in telephones 3| connected in the output of the detector.

In considering Fig. 3, assume that the signal frequency is 3105 kilocycles and that a beat frequency of about one kilocycle is desired. The crystal then should be ground for 443.43 kilo- .cycles and the triode to which it is connected has a tuned circuit 28 resonant with the fundamental frequency of the crystal and the tuned circuit 2'? resonant at the sixth harmonic, which In eachofthe circuits shown inFigs. 1-3, the frequency of the crystal can be readily determined as the quotient of the: signal frequency the'to'tal of the harmonics-used in thisu'case is"6. In Figfzithe total of the harmonics used is '5.

The fundamental is also used, makin'g aitot-al'of 6 to be the'denominator. 'In'Fig. 3'the resultant frequency is taken as one kilocycle, and the-total of the harmonics plus the fundamental 7; because of decimal fractions 'thecalculations,

however, the resultant appears from 'theformula as .99'kilocycles. The relation maybe expressed in the'equation form as:

using is to designate the crystal frequency, is, the

signal frequency, fr the resultant frequency and h the totalof the harmonics employed in conversion plus 1 if the fundamental'frequency is also used. v I

It will be noted "that the circuit of "Fig. ",3 is structurally similar to that of Fig. 2 in the series arrangement of differently tuned circuits in the oscillator plate circuit, and the coaction'of these circuits withseparate stages in the signal circuits of the receiver in similarfrequency modification functions. in results, however, becauseof the different type of signal energyprescribed in :regard to Fig. 3,

and the relative .proportionment of frequency values.

. In Fig. 4i, I have illustrated a further modification, in the, use of the crystal controlled circuits of my invention in superhetero'dyne receivers for reception through. more thanone'signal.

channel. Dual antenna and conversion systems are illustrated with ,a single crystal controlled oscillator arranged to supply the proper frequency for conversion to each system. The oscillater comprises a triode 34 having piezo-electric crystal 35 connected inthe grid circuit andtuned circuits 36 and ii! in the plate output circuit. Tuned circuit 36 is coupled with the conversion stag-ref t in the one signal channel, and tuned circuit it? with the conversion. stage "39 in the other signal channel. The outputs'of the two signal channels are fed through a common circuit resonant at the selected intermediate frequency to the remainder of the usual superheterodyne circuit, similarly as in Fig. 1.

In Fig. 4, the two antenna and conversion circults are shown by Way'of example to receive signals at 3105 kilocycles at conversion stage 38, and 5940 lzilocycles at conversion stage 39. 'The one crystal oscillator is provided with a 2835kilocycle crystal, and in the output, circuit 3K5 is tuned tothe fundamental frequency and circuit ti to the second harmonic at 5670 kilocycles. The outputs of the two conversion circuits are connected in parallel to the intermediate frequency circuit tuned to 270 kilocycles, which is the resultant frequency from both conversions. As-will from which a nominal relation of hl and H2 can be obtained by substituting appropriate desired The systems of Figs. 2 and 3 diifer be seenifrom- Fig. 4,the fundamental crystal fre-' quency will beat with the 3105 kilocycle signal and produce a -270 kilocycle wave; and likewise the 567D'kilocyclesecon'd harmonic of the crystal frequency will beat with the 5940 kilocycle'signal to produce a 270 kilocycle wave. To avoid inter-- ference in the intermediate frequency-amplifier when sign'alsat both'frequencies are received at the same time, a switching arrangement'may be provided-as at "4l,'t2, to make inoperative one or the other ofthe'receiving channels as'desire'd.

For more widely separated signal frequencies, different values of crystal frequency and different'harmonics maybe employed. A formula may be derived for determining the frequency of the crystal from the following basic relations, using fx to designate thecrystal frequency, f1 and f2 thesignal frequencies, in and hz the corresponding'harmonics of conversion, and fr the resultant intermediate frequency, which is a constant:

, a; I11 f f, f,,- .(2)

Byequating (1) and (2) (n-ir .hz=(rz ir hl (4) values for f1, f2 and fr. With the relation thus established, suitable harmonics may be selected :andthe frequency of the crystal then determined from Equation-3. Using the values shown in Fig.

4 for 11.12 and f1, the=Equation 4 reads:

5670hz'=2835h1;

onupon reducting 2h2:h1. The simplest values, there-fore, are h1=2 and h2=1, and inserting these in Equation 3 ]X is determined as Values of h1;4 a'nd" h2=2 would correspondingly require a crystal frequency of 1417.5 kilocycles.

My invention as 'hereinbefore set forth will thus'be seen to extend the adaptability of stabi- =2335 kilocycles I lized oscillations without decrease in the degree of precision obtainable infrequency conversions where-a directly stabilized fundamental oscillation is a component. The same stabilized oscillator circuit may therefore be employed to supply converting and beating oscillations, as indicated inl ig. 3, or theconverting-oscillations for a'plurality of signals of different frequencies, as indicated in Fig. 4, as well as oscillations adapted to convert ultra-high frequency signals to intermediate fr'equencydevel, as indicated in Figs. 1' and 2.

I have indicated my invention schematically for the s'akeof clearness, and the modifications illustrated intended merely as examples of the applicability of crystal controlled oscillator cir cuits in accordance with my'invention. while I have described my invention in certain preferred embodiments, I donot intend to be limited thereto. 7

For example, I may. provide a relationship of circuits in which Thus where fx is the crystal frequency, and f1 and f2 are signal frequencies. The same crystal is used for reception of both signal frequencies and only the fundamental frequency thereof is employed and harmonics of the crystal frequency are not employed.

Wherever, in the claims I refer to a piezo-electrio crystal controlled oscillator, I intend this term to include all electro-mechanical vibrators such as magneto-striction oscillators and other constant frequency devices and currents.

I desire that it be understood that other modifications may be made in my invention within the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. In an ultra-high frequency superheterodyne radio receiver, in combination, an intermediate frequency amplifier stage of fixed frequency characteristics, and a conversion oscillator circuit including piezo-electric crystal frequency control means, a plurality of output circuits, and means for independently tuning each of said output circuits for establishing different selected harmonic frequencies of oscillation relative to the natural frequency of vibration of the crystal, the natural frequency of vibration of the crystal and the harmonics thereof derived being selected with reference to the radio frequency of the received signal and the fixed frequency of operation of said intermedlatefrequency amplifier stage in said superheterodyne radio receiver for effecting conversion of the frequency of the received signal to the frequency of intermediate amplification in steps.

2. In an ultra-high frequency superheterodyne radio receiver, in combination, an intermediate frequency amplifier stage of fixed frequency characteristics, converter means, a conversion oscillator including a piezo-electric crystal and a resonant circuit tuned to the natural frequency of vibration of said crystal, an independently tuned output circuit including a split inductance component connected with said oscillator and said converter means and resonant at a selected harmonic of said crystal frequency, oscillations derived across a portion of said inductance being adapted to convert an ultra-high radio frequency in a signal to a middle frequency, and oscillations derived across the remaining portion of said inductance being adapted to convert said middle frequency to the fixed frequency of operation of said intermediate frequency amplifier stage in said superheterodyne radio receiver.

3. In an ultra-high frequency superheterodyne radio receiver, in combination, an intermediate frequency amplifier stage of fixed frequency characteristics, and a conversion oscillator circuit including piezo-electric crystal frequency control means, a plurality of output circuits, and means for independently tuning each of said output circuits for establishing different selected harmonic frequencies of oscillation relative to the natural frequency of vibration of the crystal, oscillations derived from said tuned circuits being adaptable to convert received signal oscillations of ultra-high frequency to oscillations of the fixed frequency of operation of said intermediate frequency amplifier stage in said superheterodyne radio receiver in steps beginning with the highest harmonic frequency.

4. In a superheterodyne radio receiver for continuous wave reception, a piezo-electric crystal controlled oscillator, independently tuned means for deriving an oscillation therefrom at a selected upper harmonic of the natural frequency of vibration of r the crystal, said oscillation being adapted to convert signal waves to the intermediate frequency of said superheterodyne radio receiver, and separate independently tuned means for deriving from said oscillator an oscillation at a selected lower harmonic, the last said oscillation being adapted to beat with signal waves of the intermediate frequency to produce audible notes.

5. In a superheterodyne radio receiver for continuous wave reception, a piezo-electric crystal controlled oscillator, individually tuned means for deriving oscillations from said oscillator at selected harmonic frequencies of the fundamental frequency of vibration of the crystal, and means for employing the oscillations of the crystal for progressively converting the frequency of the received wave to a resultant audible frequency for signal detection, the fundamental frequency of vibration of the crystal fx being determined by the relation:

where is is the frequency of the signal, fr is the audible frequency of detection, and h is the total of the harmonics employed in the successive conversions when the fundamental frequency is considered as the first harmonic.

6. In an ultra-high frequency superheterodyne radio receiver, in combination, an intermediate frequency amplifier stage of fixed frequency characteristics, a piezo-electric crystal controlled oscillator, and individually tuned means for de riving a plurality of oscillations from said oscillator at selected harmonic frequencies adapted for successive conversion of the signal wave to produce a desired fixed intermediate frequency; the frequency of vibration of the crystal being determined as the quotient of the signal frequency minus the desired intermediate frequency, divided by the total of the harmonics embraced by the plurality of oscillations derived from said crystal controlled oscillator.

7. In a superheterodyne radio receiver for concontinuous Wave reception, a piezo-electric crystal controlled oscillator, independently tuned means for deriving oscillations therefrom at selected harmonic frequencies of the fundamental frequency of vibration of the crystal, and means for employing the oscillations of the crystal for progressively converting the frequency of the received wave to a resultant audible frequency for signal detection, the fundamental frequency of vibration of the crystal fx being determined by the relation where is is the frequency of the signal, fr is the audible frequency of detection, and h is the total of the harmonics employed in the successive conversions plus one when the fundamental is also used.

PERCIVAL D. LOWELL. 

